1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device of a form such that the displacement operation of a piezoelectric/electrostrictive element is transmitted to a pair of right and left movable parts to control a component to be controlled, which component is sandwiched and held by the other ends of the movable parts, or the displacement operation of a pair of right and left movable parts that sandwich and hold a component to be inspected on the other end is sensed by a piezoelectric/electrostrictive element to sense the characteristics of the component to be inspected.
2. Description of the Background Art
Referring to FIG. 1, a conventional piezoelectric/electrostrictive device having such a form is constructed in such a manner that a piezoelectric/electrostrictive element 10b is disposed on each of the outside surfaces of a pair of right and left movable parts 11, 12 constituting a base 10a. Movable parts 11, 12 are connected with each other by means of a connecting part 13 on one end thereof, and movable part bodies 11a, 12a extend towards the other end thereof. The other end of movable part bodies 11a, 12a are made into mounting parts 11b, 12b for mounting a component H such as a component to be controlled or a component to be inspected.
Mounting parts 11b, 12b protrude inwards by a predetermined width from the other end of movable part bodies 11a, 12a, so as to oppose each other by holding a predetermined interval. Component H is fixed to the inside surfaces (joining surfaces) 11b1, 12b1 of mounting parts 11b, 12b via adhesives h1, h2 on the side surfaces of component H, so as to be sandwiched and held by mounting parts 11b, 12b of movable parts 11, 12.
In a piezoelectric/electrostrictive device having such a form, if component H to be mounted is long in the longitudinal direction of the device, one must increase the length L4 of mounting parts 11b, 12b, as shown in FIG. 2. In this case, the total length L1 of the device is elongated by the amount of increase in the length L4 of mounting parts 11b, 12b. Thus, if the length h of component H to be mounted is equal to the length L4 of mounting parts 11b, 12b, the total length L1 of the device is restricted by the length h of component H.
On the other hand, in the case of mounting a long component H shown in FIG. 2 to mounting parts 11b, 12b, if the length L4 of mounting parts 11b, 12b are, for example, left as it is shown in FIG. 1 without being changed, the total length L1 of the device is unchanged irrespective of the length h of component H. However, in this case, the length L4 of mounting parts 11b, 12b will be shorter than the length h of component H, thereby decreasing the area of the joining surface (bonding area) on component H. Therefore, if an ordinary adhesive made of resin is used as adhesives h1, h2, the adhesive strength on component H decreases. Decreases in the adhesive strength on component H in the worst cases cause component H to be dismounted from mounting parts 11b, 12b. 
A component H having a large dimension h in the longitudinal direction will have a mass that is increased by the amount of elongation of the length h if the other dimensions and the density thereof remain unchanged. Therefore, if the bonding area is small, for example, if mounting parts 11b, 12b are each in a state shown in FIG. 1, the impact imposed upon each of the adhesives h1, h2 will be large, whereby component H is more liable to be dismounted from each of mounting parts 11b, 12b. 
In a piezoelectric/electrostrictive device having such a form, if component H is dismounted from one of mounting parts 11b, 12b, the other of mounting parts 11b, 12b must support component H to succeed receiving the impact applied to component H. In this state, component H is liable to be dismounted from the other mounting part, and also there is a fear that the supporting balance of the mounted state may be lost to cause the one supporting mounting part or the movable part connected thereto to be broken by the action of torsional force.
In order to meet this problem, one must use an adhesive having an extremely high adhesive strength; however, it is generally difficult to obtain a special adhesive that can ensure a sufficient adhesive strength no matter how small the bonding area is. Furthermore, there is naturally a limit even in the case of using an adhesive having such a special property.
In a piezoelectric/electrostrictive device having such a form, in the case of improving the device properties by increasing the displacement of mounting parts 11b, 12b, one must increase the amount of displacement of the movable part bodies 11a, 12a by increasing the length of the movable part bodies 11a, 12a of movable parts 11, 12. However, in order to increase the length of the movable part bodies 11a, 12a of movable parts 11, 12 without increasing the total length L1 of the device, one must reduce the length of mounting parts 11b, 12b. As a result of this, the bonding area of joining surfaces 11b1, 12b1 at the mounting parts 11b, 12b will be smaller to weaken the adhesive force of component H to joining surfaces 11b1, 12b1 of mounting parts 11b, 12b all the more, whereby component H will be more liable to be dismounted and drop off from joining surfaces 11b1, 12b1.
In a piezoelectric/electrostrictive device having such a form, in order to mount component H onto mounting parts 11b 12b of movable parts 11, 12, component H is bonded to joining surfaces 11b1, 12b1 generally through the intermediary of adhesives h1, h2 made of resin. However, adhesives h1, h2 made of resin will have a reduced hardness or reduced Young's modulus when the temperature changes above room temperature. The temperature change of the state of use of piezoelectric/electrostrictive devices is, for example, of a degree within a range from room temperature to 100° C. However, even in this temperature range, adhesives h1, h2 will be softened at a high temperature. For this reason, the distortion of adhesives h1, h2 when an external force is applied will differ greatly between the state of room temperature and the state of a higher temperature than this. Therefore, the device properties of the piezoelectric/electrostrictive device having this form will differ greatly at a state of high temperature, even though the device properties in a state of room temperature remain as originally set.
FIGS. 3 and 4 illustrate the operation state of the device at a low temperature such as room temperature and at a higher temperature than room temperature, respectively. The influence caused by such a temperature change (temperature variation) will be larger accordingly as the bonding area is smaller, because the distortion imposed upon the adhesive will be larger accordingly as the bonding area is smaller. Therefore, as the bonding area increases, the influence of the temperature variation will be smaller.
In a piezoelectric/electrostrictive device having such a form, if component H increases in size to increase its mass, fixing part 13 for fixing the device itself must support the combined mass of component H and the device itself. Therefore, if an impact is received, fixing part 13 is liable to be dismounted. If the length L2 of fixing part 13 is increased in order to increase the bonding area, the total length L1 of the device will also increase.